This invention relates to the field of recessed sputter targets and particularly to a method of manufacturing recessed sputter targets.
In the field of sputter target manufacture, various means bond the target material to the backing plate. Historically, target manufacturers soldered targets to backing plates. As sputtering temperatures increased and target sizes increased, soldering failed to provide the necessary bond in view of the following disadvantages: 1) low melting temperatures limited chamber operating temperature; 2) the solder""s high vapor pressure introduced impurities into the chamber; and 3) low bond strength, particularly at elevated temperatures, resulted in occasional bond failures. Since a debonded target can destroy not only a wafer, but also its supporting electrostatic chuck, it""s most important to avoid bond failures. In fact, bond integrity is so important to sputter target manufacturers that Hunt et al., in U.S. Pat. No. 6,092,427, developed a specialized method for preparing and testing bond interface evaluation samples. This method evaluates the strength of bonds between a sputter target and a backing plate. A sample of the material is removed through a first opening formed at one end and a threaded opening formed to split the first opening into two openings. Threading these openings and pulling the threaded openings measures the bond strength.
In view of the above problems, commercial target manufacturers have proposed several solutions for achieving a solid bond. For example, H. Zhang, in U.S. Pat. No. 6,071,389, discloses the use of a titanium interlayer to diffusion bond a cobalt target to an aluminum or copper backing plate. The process deposits the titanium interlayer by electroplating, sputtering, electroless plating or plasma spraying. The deposited titanium bonds to both the cobalt and the backing plate material. This process also relies upon machining grooves into the target and backing plate to further improve bonding.
Hunt et al., in U.S. Pat. Nos. 5,836,506 and 6,073,830 disclose a method for roughening a cylindrical target""s back and side surfaces and diffusion bonding the target""s back and side surfaces to a backing plate. This method forms a solid state bond and has proven most effective for securing a target to a backing plate. Unfortunately, since the target sputters preferentially from the center, the cylindrical target""s yield or use during sputtering is far less than one-hundred percent. The low yields resulting from preferential center region sputtering leave an opportunity for improved target utilization.
The method manufactures sputter target assemblies. It first includes the step of manufacturing a target insert. The target insert has a yield strength, a diameter, a height, a planar top surface and a conical-shaped rear surface. Then a backing plate is manufactured. The backing plate has a cylindrical recess that corresponds to the diameter of the target insert. The cylindrical recess has a depth less than the height of the target insert and a yield strength less than the yield strength of the target insert. Finally, pressing the target insert into the cylindrical recess of the backing plate bonds the target insert to the backing plate to form a target assembly. The pressed target assembly contains the target insert with the conical-shaped rear surface.
The sputter target assembly includes a cylindrical backing plate. The cylindrical backing plate has a planar front surface and a recess within the front surface. A target insert bonds to the backing plate within the recess of the backing plate. The target insert has a planar front surface and a rear surface. The rear surface has at least about fifty percent of its surface area conical-shaped or tapered. The rear surface bonds to the backing plate to secure the target insert to the backing plate and form the target assembly.